Foaming of polystyrene in a high frequency field



Sept. 12, 1967 MANUEL 3,341,638

FOAMING OPPOLYSTYRENE IN A HIGH FREQUENbY FIELD Filed Sept. 14, 1965 2Sheets-Sheet 1 INVENTOR HELMUT MANDEL ATT p 12, 6 H. MANDEL 3,341,333

FOAMING OF POLYSTYRENE IN A HIGH FREQUENCY FIELD Filed Sept. 14, 1965 2Sheets$heet INVENTOR LMUT M NDE United States Patent 3,341,638 FOAMINGOF POLYSTYRENE IN A HIGH FREQUENCY FIELD Helmut Mandel, Reibach uberDieburg, Germany, assignor to Dorplastex A.G., Zug, Switzerland, acorporation of Switzerland Filed Sept. 14, 1&65, Ser. No. 487,244 3Claims. (Cl. 264-25) In the manufacture of composite board material,with foam polystyrene as core layer, and any paneling material, forexample PVC panels, prior to foaming in the electric field of a highfrequency generator, it is necessary to humidity the pre-foamedparticles of polystyrene with a wetting agent or an electrolytedissolved in water, for

erator.

More specifically, the pre-foamed particles, dispensed into the form,are humidified continuously by means of stationary or movable nozzles.

Humidification of thicker layers can be produced in the intervalsbetween, or substantially simultaneously with the invention.

FIG. 2 illustrates single foam layer.

FIGS. 3, 4, and 6 show the invention applied to a sequence of foamlayers and FIG. 7 represents a modification of the process illustratedin FIGS. 3, 4, 5 and 6.

As shown in FIG. 1, box form 1 moving in direction 2 contains a layer 3of prefoamed particles which are humidified by being passed under anumber of nozzles 4 fed over line 5 from vessel 6. A pump 7 may be usedto produce the necessary pressure, unless the liquid in vessel 6 isalready under appropriate pressure. Three-way valve 7 may provideinjection of an additive from line 8 to control the spraying process.Valve 10 represents another control device.

According to FIG. 2, pre-foamed by means of a spraying device ordispenser in a layer of an application of the invention to a foamedpolystyrene is humidified by means of dispensing the pre-foamed polybymeans of nozzle 14', the reconstant speed in direction 16 into theposition shown in FIG. 4.

In a subsequent step, as shown in FIG. 4, belt 13 moves into theopposite direction indicated at 17, whereby an Patented Sept. 12, 1967additional .4" pre-foamed polystyrene layer is produced, superimposed onlayer 15. Here no humidification takes place, and we arrive at theposition shown in FIG. 5.

In another spraying operation, With box 15 again moving in direction 16,as shown in FIG. 6, another layer 18 is added anda total height offoamable material of say 1.2" is reached.

During this third spraying process, however, the material will behumidified by means of the nozzle 15. Thus, during these three sprayingsteps providing a thickness of .4" each, only the first and the lastlayers 15 and 18 are humidified as respect to FIGS. 3, 4, 5 and 6.However, by mounting a second nozzle, schematically indicated at 21, onthe other side of nozzle 14, in principle, each layer can be humidifiedduring each spraying step.

As apparent from FIG. 7 the box form 12 containing the severalsuperimposed layers of foamable material, is moved by belt 13immediately after humidification into the clamping or haltering device,schematically indicated at 22, and the plates 24 and 25 of which alsoform the electrodes of a dielectric heater, connected to a highfrequency generator (not shown). In this way, the foaming is efiectedimmediately after humidification.

In this case also, in order to prevent overheating, only one or more ofthe upper or outer layers of the foamable material need to behumidified.

Generally, humidification in accordance with the invention has thefollowing features or advantages.

In the manufacture of composite boards or similar process. With dryproduce a denser layer.

Pre-humidified pre-foamed polystyrene is not as easily dispensable andan additional pressing or stamping operation may become necessary.

With this type of humidification also a separate humidiin the highfrequency field already melts in the high heat, while the border areasare not yet sufliciently welded together.

While the invention has wit parting from the scope of this disclosure.

I claim:

1. In a method of forming foamable polystyrene material into panels, thesteps of continuously injecting said material by spreading it from thetop onto a box form while said box form is moving forward and backwarddissolved electrotype during said spreading, and exposing said layers toa dielectric field immediately after spreading and humidification.

3,341,688 3 4 2. l\fIet hod according to claim 1 comprising the step of3,037,897 6/1962 Pelley 264-47 g fiy gg y g w other y h f 3,197,5317/1965 Wilbur 264-88 et 0 accor ing to c aim 1 comprising t e step 0humidifying ,at least one of the outer layers to increase OTHERREFERENCES strength at outer portions of the foam. 5 PlasticsEngineering Handbook, 3rd edition, 1960,

pages 181 and 180 relied upon. References Cited ROBERT F. WHITE, PrimaryExaminer.

UNITED STATES PATENTS 264-25 R. B. MOFFITT,-Assistant Examiner.

2,951,260 9/1960 Harrison 2,998,501 8/1961 Edberg 1 1- 264-26 10

1. IN A METHOD OF FORMING FOAMABLE POLYSTYRENE MATERIAL INTO PANELS, THESTEPS OF CONTINUOUSLY INJECTING SAID MATERIAL BY SPREADING IT FROM THETOP ONTO A BOX FORM WHILE SAID BOX FORM IS MOVING FORWARD AND BACKWARDRELATIVE TO THE POINT OF INJECTION, SO AS TO FORM A NUMBER OFSUBSTANTIALLY CONTINUOUS LAYERS, ONE SUPERIMPOSED UPON THE OTHER;HUMIDIFYING AT LEAST SOME OF SAID LAYERS WITH DISSOLVED ELECTROTYPEDURING SAID SPREADING, AND EXPOSING SAID LAYERS TO A DIELECTRIC FIELDIMMEDIATELY AFTER SPREADING AND HUMIDIFICATION.